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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Sphenopus Trin.

From the Greek sphen (wedge) and pous (foot), in reference to the distally thickened pedicels.

Type species: Type: S. gouani Trin., nom. illeg..

Habit, vegetative morphology. Annual; caespitose. Culms (4–)7–30 cm high; herbaceous; 1–3 noded. Culm nodes exposed, or hidden by leaf sheaths; glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Sheath margins free. Sheaths not keeled, terete. Leaf blades linear; apically cucullate; narrow; 0.3–0.6 mm wide (in S. divaricatus); flat to folded (to almost filiform); without cross venation; persistent. Ligule an unfringed membrane; not truncate; 0.6–3.4 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate (with numerous, very small spikelets); open; with conspicuously divaricate branchlets; with capillary branchlets to without capillary branchlets. Primary inflorescence branches borne distichously. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; long pedicellate (the pedicels claviform).

Female-fertile spikelets. Spikelets 1.5–2.8 mm long; elliptic; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous or minutely aculeolate); the rachilla extension naked. Hairy callus absent. Callus short; blunt (glabrous).

Glumes two; minute to relatively large (G1 0.2–0.4 mm long, G2 0.5–0.9 mm in S. divaricatus); very unequal; shorter than the spikelets; shorter than the adjacent lemmas; not pointed (emarginate, truncate or rounded); awnless; carinate; very dissimilar to similar (hyaline to membranous, rounded to emarginate, the lower smaller). Lower glume 0 nerved, or 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 2–7. Lemmas similar in texture to the glumes (membranous, with hyaline margins wider above); not becoming indurated; entire; pointed, or blunt; awnless; hairless; glabrous; non-carinate (but keeled on all three veins); 3 nerved; with the nerves non-confluent. Palea present; relatively long; tightly clasped by the lemma; entire, or apically notched; thinner than the lemma to textured like the lemma (hyaline); 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 3. Anthers 0.2–0.6 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea, or free from both lemma and palea; small (1–1.2 mm long in S. divaricatus); oblong or ellipsoid; shallowly ventrally longitudinally grooved; compressed laterally, or not noticeably compressed. Hilum short. Endosperm liquid in the mature fruit, or hard; with lipid. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs (usually), or not paired (solitary); silicified (when paired), or not silicified. Costal short-cells predominantly paired. Costal silica bodies horizontally-elongated smooth, or tall-and-narrow, or crescentic; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous (rarely), or not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (not apparent in the large-celled epidermis, save for the ‘midrib hinges’). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 6 and 7. 2n = 12 and 24. 2 and 4 ploid. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Parapholiinae. 2 species.

Distribution, phytogeography, ecology. Mediterranean to western Asia.

Commonly adventive. Species of open habitats; halophytic. Saline soils and maritime sand.

Rusts and smuts. Smuts from Tilletiaceae. Tilletiaceae — Tilletia.

References, etc. Leaf anatomical: studied by us - S. divaricatus (Gouan) Reichenb., Sphenopus ‘sp.’.

Special comments. Fruit data wanting. Illustrations. • General aspect (S. divaricatus): Gibbs Russell et al., 1990. • S. divaricatus (as S. gouani: Coste (1906), Fl. France 3. • Inflorescence detail (S. divaricatus). • Inflorescence detail (S. divaricatus). • Spikelet (S. divaricatus)

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.